I went the AVR route because he asked for 2.1. There are (IMO) no "computer speaker" sets that will match my recommendation.
As to real-estate... well, you are gonna need amps, a crossover, and (likely) a DAC.
I suppose you could you powered speakers (the poster stating that the difference between the 2030P and 2030A is that the A has an amp is correct), split an RCA out from your computer, use a passive in-line crossover, and attach the subs, drivers, and assorted power cables... but it seems simpler to make a shelf for your AVR.
I went the sub route because he asked for 2.1. I don't see a way to get nearly the bass response out of a $300 pair of bookshelves that you'll get out of a $100 pair of bookshelves and a used sub.